Internal core lifters are used within a mold device to mold and eject undercuts in plastic injection molds. An internal core lifter generally consists of a core blade seated at a predetermined angle achieved by mounting one end of the core blade at a fixed angle to a coupling which then slides linearly along a support mounted to the mold ejection plates. These internal core lifters are custom designed to fit specific molds on a case by case situation.
In order to mold undercuts and eject plastic parts, the core lifter has a core blade that is attached to one ejector system of the mold, and the opposite end of the core blade is used to mold and eject the plastic part. To mold undercuts, the core blade is placed at an angle determined by the mold designer. Since one end of the core blade is configured to mold the undercut of the plastic part, the core blade is required to move horizontally away from the undercut during a vertical ejection of the plastic part. This horizontal movement is necessary during ejection so as not to damage the plastic part.
The amount of undercut, horizontal displacement required and the ejector system's requisite travel distance determines the angle at which the internal core lifter is seated. After the mold designer has determined the necessary angle for the internal core lifter, it was customary to make a specially designed and manufactured internal core lifter. Many times, the internal core lifter was a one time design. These one time designs are expensive to have built because special made internal core lifters require more research and development and manufacturing costs. These costs are generated because each core lifter is a new project requiring special tailoring of the components to the specific mold with which it is going to be placed.
Specifically, an internal core lifter generally comprises a core blade, an angle seating junction and a support. The core blade usually has an end configured for molding plastic parts, and an opposite end for seating at a desired angle. The core blade is easily cut to the desired length which varies from mold to mold. However, the angle seating junction is not capable of being adjusted from mold to mold. The core blade is fixed at this desired angle by either machining a heel or bolting it to a heel plate at the angle. This welding or bolting permanently fixes the angle at which the core blade is attached. Then using the heel plate the core blade is placed in cooperation with the support plate which is designed to provide linear movement for the core blade. Additionally, the support plate attaches the internal core lifter to the mold in which it is being used. Because the various molds often have a different seating angle, and the angle at which the core lifter is seated is fixed, a specially made core lifters are provided for the several different molds.
When using specifically designed internal core lifters, the mold maker must make the internal core lifter to fit the desired angle of the particular mold. Sometimes the angles are odd angles, which an internal core lifter manufacturer would have no reason to stock because of it being too expensive to inventory such a seldom used angle.
Alternatively, the core blade is pivotally mounted to a coupling which is placed in cooperation with a support plate to guide the coupling's lateral movement. A pivotal mount provides for a range of angles through which the core blade is capable of being seated, and the support plate provides for linear movement. However, the disadvantages are directed toward the durability of this internal core lifter. The pivotal mount is generally done using a pin or circular dowel configurement. In molding, a large amount of force is transferred through the core lifter. This force is required for successful molding to completely fill the steel cavities with plastic, thus forming a correct plastic part. In this arrangement, the large force is transferred through the core lifter which requires the transfer of force through the pivotal mount. The lack of sufficient surface area over which to distribute the molding force when the molding force is transferred between the connecting elements of the pivotal mount creates a large concentration of pressure which in turn may cause conventional pivotal mount methods to fail or to wear excessively. Because of a lack of surface connection area in previous pivotal mount methods, the durability of the core lifter is substantially reduced using this method. When the internal core lifter fails, it can cause damage to the molding process, such as deformed plastic parts and damage to the mold itself.
Previously used core lifters using a dowel type arrangement to pivot the core blade have been unacceptable due to its lack of durability. The core blade requires a high component of durability in order to withstand the forces created in molding operations. Thus, it is undesirable to use pivot connections which do not efficiently and effectively transfer the force.
The present invention is directed toward a new and improved universal internal core lifter which can effectively mold and ejects plastic parts from a mold without having to be specially manufactured for specific angles. A further object is to have an universal internal core lifter that is durable. These and other objects will become apparent from the following detailed description and the appended claims.